In modern day electronics, a single electronic device may require multiple forms of electrical power, such as alternating current and direct current. Additionally, the electronic device may make use of several different voltage levels. For example, in a personal computer, there may be a need for +3.3 V, −5 V, +5 V, and +12 V to provide different circuits in the personal computer with required power. Similarly, in a portable electronic device powered by a battery source, there is often a need to provide voltage levels that differ from the voltage level of the battery source. Furthermore, the voltage level of the battery source may decrease as the battery source discharges, while the circuitry in the portable electronic device may typically require a constant voltage level.
The conversion of electrical power from a first voltage level to a second voltage level may introduce an unwanted frequency component in the power signal at the second voltage level. The unwanted frequency component may be related to the switching frequency of the voltage converter. In some cases, the switching frequency may negatively affect the operation of the electronic device. For example, in portable communications devices, there are certain frequencies that manifest in the form of audible noise. Therefore, it is desirable that the switching frequency of the voltage converter and its harmonics should not lie within these frequencies. Switching frequencies and harmonics containing these audible frequencies may produce noise that may be noticeable as humming, clicking, buzzing, and so forth, for instance. Similarly, if the electronic device plays video, it may be possible to visually detect some artifacts of the switching frequency in the video images or the lighting of the display that is displaying the video.
A commonly used technique to control the switching frequency of a voltage converter is to use pulse-width modulation (PWM) control. With PWM control, the switching frequency is known, therefore, the switching frequency may be set so that the switching frequency and its harmonics do not contain frequencies that may produce detectable noise. However, PWM control may require a relatively complex feedback control system to ensure converter stability, therefore incurring greater development and manufacturing costs.